Hibernate version:2.1.6

i have two abstract class:AbstractClient and AbstractCard.
AbstractClient has two child class:PersonalClient and GroupClient
AbstractCard has two child class:NormalCard and SpecialCard

relationship of AbstrcatClient and AbstractCard is one to many. in AbstractCard has a HashSet of AbstractCard. I map two abstract class using subclass.

The problem is insert procedure is correct.but when i get a PersonalClient instance and get its AbstractCard collection, the size of HashSet always show 1. There should be many records in my database.

Who meet the same problem. Thanks for any help!